1. Field of the Invention
The present invention relates to a scan line driving method for a thin film transistor liquid crystal display (TFT LCD). More particularly, the present invention discloses a method that enables the simultaneous driving of two scan lines in a TFT LCD.
2. Description of the Prior Art
Thin film transistor liquid crystal displays (TFT LCD) are thin, flat panel display devices that can be found in a plethora of electronic goods, ranging from notebook computers and digital cameras, to flight avionics and medical diagnostic tools. TFT LCDs offer crisp, high-resolution images, and have the primary advantage of offering relatively low power-consumption rates while still maintaining good color contrast and screen refresh rates.
Please refer to FIG. 1. FIG. 1 is a simple block diagram of a TFT LCD 10. The TFT LCD 10 is composed of a plurality of pixels 12 that are regularly arrayed in a rectangular manner, forming rows 10R and columns 10C of pixels 12. A particular pixel 12 consequently has a location within the TFT LCD 10 that may be referenced in a Cartesian manner by the row 10R and column 10C in which that particular pixel 12 is located.
Please refer to FIG. 2 with reference to FIG. 1. FIG. 2 is an equivalent circuit diagram 20 for the TFT LCD 10. Each pixel 12 has a circuit equivalent of a driving transistor (TFT) 24 and two capacitors 22a and 22b, which are electrically connected between the driving transistor 24 and a common electrode 26. The common electrodes 26 may be thought of as a sort of ground, common to all of the pixels 12. Capacitor 22a is a circuit equivalent of the TFT array substrate that is used to form the pixels 12. Generally speaking, the capacitor 22a is insufficiently large to maintain a driving voltage of the pixel 12 for a suitable length of time. Hence, capacitor 22b is provided so that the liquid crystal in the pixel 12 is able to retain the charge associated with a first driving signal until a second driving signal is received. Each driving transistor 24 is further connected to a scan line 28R and to a data line 28C. Each row 10R has a respective scan line 28R, and each column 10C has a respective data line 28C. All driving transistors 24 in the same row 10R are connected to the same respective scan line 28R. Similarly, all driving transistors 24 in the same column 28C are connected to the same respective data line 28C. As noted above, each pixel 12 has a unique address given in row 10R and column 10C coordinates. To turn on or turn off a pixel 12, an appropriate voltage is placed upon the data line 28C corresponding to the column 10C in which the pixel 12 is located, and a scanning voltage is placed upon the scan line 28R corresponding to the row 10R in which the pixel 12 is located, which activates the driving transistor 24 of the pixel 12 to charge or discharge the capacitors 22a and 22b according to the voltage placed upon the data line 28C. Changing the voltage across the capacitors 22a and 22b attenuates the visual characteristics of the pixel 12, and in this manner the entire display 10 may be changed at will on a pixel-by-pixel basis.
Due to leakage currents, the capacitors 22a and 22b must be regularly refreshed to maintain their appropriate voltages, and hence maintain the display integrity of the TFT LCD 10. Typically, this is performed at something like 60 times per second, and is performed a row 10R at a time. Data line drivers 29C are energized according to the display characteristics of each respective pixel 12 in a selected row 10R to activate the data lines 28C. The scan line 28R for the row 10R is then activated by scan line circuitry 29R, while all other scan lines 28R are kept in an inactive state. An entire row 10R is thus written to at once, and the process is repeated for a succeeding row. Note that it is not possible to simultaneously write to two or more rows 10R at a time, as a single signal data line 28C is used to drive a plurality of column pixels 12. When performing the refreshing process, sufficient time must not only be allowed for the charging/discharging of the capacitors 22a and 22b, but also for the settling of the data drivers 29C. Rapid activation of scan lines 28R before the data lines 29C have settled can lead to inappropriate values being written into the capacitors 22a and 22b within a row 10R, leading to image degradation of the TFT LCD 10. Similarly, allowing insufficient time for the charging of the capacitors 22a, 22b will lead to an inappropriate voltage across the capacitors 22a, 22b, and thus to image degradation. Consequently, signal timing for the data lines 28C and scan lines 28R is very important.
As resolutions increase (i.e., the number of rows 10R and columns 10C increases), it becomes more and more difficult to refresh the TFT LCD 10, as the same amount of time (i.e., {fraction (1/60)}th of a second) must be divided over more and more rows 10R. This leaves less and less time for the settling of the data drivers 29C (which have to drive greater numbers of pixels 12), and for the actual refreshing of the capacitors 22a, 22b. Several solutions have been proposed that have enabled TFT LCDs to support increasingly higher numbers of pixels, such as U.S. Pat. No. 6,081,250, which is incorporated herein by reference. However, in the proposal of U.S. Pat. No. 6,081,250, the data driving circuit has a special design that is not compatible with conventional data drivers.
It is therefore a primary objective of this invention to provide a driving method and associated TFT LCD that enables extended row scanning durations. It is a further objective of this invention to provide simplified scan line circuitry in a TFT LCD.
Briefly summarized, the preferred embodiment of the present invention discloses a driving method and an associated thin film transistor liquid crystal display (TFT LCD). The driving method utilizes a TFT LCD comprising a plurality of pixels arrayed as a plurality of rows and a plurality of columns. For a first pixel located at a first row, first column position (R1, C1), and a second pixel located at a second row, the first column position (R2, C1), the first pixel is addressable by a first scan line corresponding to the first row (R1), and a first data line corresponding to the first column (C1), and the second pixel is addressable by a second scan line corresponding to the second row (R2), and a second data line corresponding to the first column (C1). The method comprises setting the first data line to a first pre-determined voltage corresponding to a desired display state of the first pixel. The second data line is set to a second pre-determined voltage corresponding to a desired display state of the second pixel. Subsequently, the first scan line and the second scan line are simultaneously set to a scan voltage. To effect this, the first scan line and the second scan line share the same scan line driver.
It is an advantage of the present invention that by providing for the simultaneous activation of two scan lines, extended row scan line durations are made possible, while also simplifying the scan line driving circuitry.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment, which is illustrated in the various figures and drawings.